1. Field of the Invention
The present invention relates to an etchant used in the manufacture of semiconductor devices and to an etching method which uses the etchant. More particularly, the present invention relates to a nitride film etchant that can be used at low temperatures in the manufacture of semiconductor devices, and to an etching method which uses the nitride film etchant.
2. Description of the Related Art
Nitride films, in particular, silicon nitride films, are physically and chemically stable, and are thus often used in the manufacture of semiconductor devices. For example, such films are increasingly used as insulating films and capacitor dielectric films, as well as etch stop films during the etching of silicon oxide films. Typically, silicon nitride films have a higher dielectric constant and a higher mechanical hardness than silicon oxide films, and excel in preventing vapor and sodium from being diffused into under layers of the silicon nitride films. Also, silicon nitride films are not prone to the generation of pin hole defects. For these and other reasons, the use of silicon nitride films is increasing.
However, the physical and chemical stability of silicon nitride films also makes them relatively difficult to etch. Also, silicon nitride films must often be etched while maintaining a high etch selectivity with respect to a silicon oxide film or a polysilicon film. For example, as mentioned above, silicon nitride films are frequently used as an etch mask in an etch process for patterning silicon oxide films. In such cases, after the silicon oxide film is etched, the silicon nitride film which was used as an etch mask is typically etched by a wet etching method.
In an existing wet etching process, a wafer having a silicon nitride film thereon is introduced into an etching bath containing phosphoric acid (H3PO4) of 85% by weight to selectively etch the silicon nitride film while maintaining a high etch selectivity of about 20% or greater with respect to a silicon oxide film. The etching bath is heated to a high temperature of about 160-170xc2x0 C. In this wet etching process, the etch rates of a silicon nitride film and a silicon oxide film are about 40 to 45 xc3x85/min and 1.2 to 2.0 xc3x85/min, respectively, and the etch selectivity between the silicon nitride film and the silicon oxide film is about 26.56.
When etching a silicon nitride film through wet etching, the aforementioned high temperature is applied in order to increase the etch rate of the silicon nitride film. This is in consideration of the fact that the etch rate of a typical silicon nitride film is proportional to the applied temperature.
However, when a high temperature condition is applied as in the existing wet etching process, it is difficult to maintain the concentration of the H3PO4 solution at a desired value. That is, at a high temperature, the concentration of an etchant increases since the moisture contained in the etchant readily evaporates, thus causing a difference between the desired concentration of the etchant and the actual concentration of the etchant contained in an etching bath. Thus, when a silicon nitride film is etched at 160-170xc2x0 C., deionized (DI) water must be continuously supplied to maintain the concentration of phosphoric acid in the etchant at a level which produces the required process condition. Furthermore, in this case, chemical matter (phosphoric acid) is partially evaporated as well, although at lesser quantities than the moisture. Thus, the chemical itself must also be continuously supplied.
High concentrations of H3PO4 etchant caused by the evaporation of moisture can damage etching equipment, thus serving as a factor which shortens the life span of the etching equipment. Improper concentrations of H3PO4 etchant can also adversely effect etching time and effectiveness. However, the continuous supply of different quantities of DI water and chemical to avoid such improper concentrations of H3PO4 etchant is difficult to accurately control.
Therefore, an etchant having a new composition is desired which is capable of etching a nitride film at a low temperature while maintaining a high etch selectivity between the nitride film and an oxide film.
An object of the present invention is to provide an etchant used in the manufacture of semiconductor devices, the etchant capable of etching a nitride film at a high etch rate and a low temperature while maintaining a high etch selectivity between the nitride film and an oxide film.
Another object of the present invention is to provide a method of etching a nitride film using the above-described etchant.
To achieve the first object, the present invention provides an etchant for a nitride film used in the manufacture of semiconductor devices, wherein the etchant is a water solution containing phosphoric acid (H3PO4) of a concentration of 50-70% by weight and hydrofluoric acid (HF).
Preferably, the concentration of HF in the etchant is 0.005-0.05% by weight.
To achieve the second object, the present invention provides a method of etching a nitride film, wherein a wafer having a nitride film formed thereon is introduced into a bathing tube containing an etchant which is a water solution containing phosphoric acid (H3PO4) of a concentration of 50-70% by weight and hydrofluoric acid (HF), and wherein the nitride film is etched by the etchant.
It is preferable that the temperature of the etchant is 130xc2x0 C. or less. More preferably, the temperature of the etchant is 100 to 120xc2x0 C.
Preferably, the concentration of HF in the etchant is 0.005-0.05% by weight.
According to the present invention, the etch rate of a nitride film can be increased compared to the prior art by setting the concentration of phosphoric acid to be, preferably, 50-70% by weight when etching the nitride film using an etchant including phosphoric acid and hydrofluoric acid. Preferably, the composition of the hydrofluoric acid is set to be 0.005-0.05% by weight. Accordingly, the etchant according to the present invention can etch a nitride film faster than the prior art even at a temperature of 130xc2x0 C. or less, which is lower than the temperature in the prior art. Also, the etchant according to the present invention can maintain a higher etch selectivity between an oxide film and the nitride film than that in the prior art.
To achieve the first object, the present invention also provides an etchant for a nitride film used in the manufacture of semiconductor devices, wherein the etchant is a water solution containing hydrofluoric acid (HF) of a concentration of 0.05% by weight or less and phosphoric acid (H3PO4).
Preferably, the concentration of HF in the etchant is 0.005-0.05% by weight.
It is preferable that the concentration of H3PO4 in the etchant is 50-70% by weight.
To achieve the second object, the present invention also provides a method of etching a nitride film used to manufacture semiconductor devices, wherein a wafer having a nitride film formed thereon is introduced into a bathing tube containing an etchant which is a water solution containing hydrofluoric acid (HF) of a concentration of 0.05% by weight or less and phosphoric acid (H3PO4), and the nitride film is etched by the etchant.
It is preferable that the temperature of the etchant is 130xc2x0 C. or less. More preferably, the temperature of the etchant is 100 to 120xc2x0 C.
Preferably, the concentration of HF in the etchant is 0.005-0.05% by weight, and the concentration of H3PO4 in the etchant is 50-70% by weight.
According to the present invention, an etchant including phosphoric acid and hydrofluoric acid can etch a nitride film faster than the prior art at a temperature of 130xc2x0 C. or less (more preferably, 100-120xc2x0 C.) which defines a temperature range that is lower than the prior art, by setting the concentration of hydrofluoric acid to be 0.05% or less. Also, addition of hydrofluoric acid at the above-mentioned concentration increases the etch rate of a nitride film and increases the etch selectivity between an oxide film and the nitride film. Furthermore, when the concentration of phosphoric acid is set to be 50-70% by weight, the etch rate of the nitride film further increases.